Baffling fuelling/electronic problems E30/M20 320i [long]

1985 E30/M20 320i 170k miles

Car has run faultlessly for 5 years, 50k+ miles, regularly serviced and
never had engine problems. Until …

Filled up with petrol on a Friday evening, drove home without problems.
Started OK on the following Monday morning and ran fine for around a
mile. Then …

Engine started running very rough, no power, kept stalling, fuel pump
noisy, strong smell of petrol. Limped home, had a look under the bonnet,
only visible fault was a slight weep of petrol from the injector seal on
the No 6 cylinder. Ran the engine for 15 minutes at a high idle and it
seemed to settle down, but within a few miles started having the same
symptoms again.

I suspected that the temperature sensor was faulty, so left the car at a
local garage who concluded the same and replaced the sensor. No
improvement. They replaced some suspect air hoses and the fuel filter but
nothing made any difference. After several days of trying everything they
could think of, they could not find a fault. The only fix they had was to
put a bulb in parallel with the sensor to reduce the resistance and fool
the engine into thinking it was warm. This fixed most of the running
problems (with a few tweaks to get the emissions back to normal)

However, the fuel pump is still noisy, and the car is obviously difficult
to start from cold. There is also some slight hesitation on the overrun
at around 2000 to 2500 rpm. Fuel economy is as it was before, steady
cruising at speed is as before, but acceleration seems a little sluggish
sometimes.

I have tried checking out all of the electrical connections but have
found nothing corroded or broken. I have pulled all of relays and fuses
to clean the contacts but again no improvement.

I am tempted to replace the fuel pump (even though the garage found that
it was pumping at the correct pressure despite the noise). Maybe replace
the fuel pump relay (cannot see why this would give these problem
though). Engine management unit? Seems like an expensive thing to try on
the off chance. Oh, I have refilled the tank several times with from a
different petrol station, so I do not think it is the fuel itself.

The car is being replaced early next year, so I am not overly concerned
(apart from the annoyance factor of the fuel pump noise!), but I do not
like mysteries and would like to get to the bottom of this problem :-)

Sorry for the long post …

Any ideas out there?

Cheers,

Al.

Update:

Hmmm ...

A few days ago the fuel pump stopped making noises. I couldn't get the
engine to run, so removed the bulb in parallel with the temperature sensor.

Now the car runs perfectly!

So, was the fault with the fuel pump, the fuel, or some random electronic
fault ...

My guess is that the fuel added just before the problems was to blame
(water in the supply?). Once enough 'clean' fuel had flushed the crap out
everything returned to normal.

Still a mystery, but at least the car runs like a dream again :-)

Al.